The negative electrode (anode) of a typical high energy lithium battery typically comprises one or more of a variety of any suitable lithium-containing substances such as metallic lithium, lithium metal alloys, or lithium metal oxides. A variety of positive electrode (cathode) materials can be used including lithium vanadium oxide. The electrodes are coupled using a liquid electrolyte or a solid electrolyte. Liquid electrolytes include nonaqueous solutions and molten salts. Solid electrolytes include ionically conducting polymers. During operation, lithium ions go into and out of the vanadium oxide structure (intercalation). More specifically, as the battery is discharged, lithium is oxidized at the anode and lithium ions move into the electrolyte and to the cathode. When the battery is charged lithium ions are reduced (plated) at the anode. This is accompanied by movement of lithium ions into the electrolyte from the cathode.
The cathode material should have a high specific capacity as well as good chemical and electrochemical stability such that it can endure many long cycling operations. The method of preparation of the cathode material can affect one or more of these characteristics. This is typically because the method of preparation affects the particle size, particle size distribution, level of crystallinity, and purity of the cathode material.
Lithium vanadium oxide can be made by a variety of methods. One such method involves mixing a lithium ion-containing compound and vanadium pentoxide and then heating the mixture to a temperature sufficient to form molten material (typically about 700.degree. C. to about 800.degree. C.). This molten material is then cooled to form solid lumps that are mechanically ground into a powder. These lumps can be very difficult to grind to a material of suitable particle size and particle size distribution. Special handling procedures are also typically required for such melt processes. Furthermore, the molten lithium vanadium oxide can react with the container and contaminate the product.
Nonmolten methods have been developed in an attempt to avoid the problems associated with molten methods. Many involve the use of liquids (e.g., solvents). For example, U.S. Pat. No. 5,039,582 (Pistoia) discloses a method for making amorphous lithium vanadium oxide from lithium hydroxide and vanadium pentoxide in water. This reaction is carried out at room temperature or with moderate heating. The product is collected by precipitation and then dried at 100.degree. C. to 200.degree. C. Although this patent describes the product as a very fine precipitate, many methods that use lithium hydroxide in water produce a gel that is difficult to filter, dry, and grind. To solve this problem, U.S. Pat. No. 5,549,880 (Koksbang) discloses a process that involves dispersing lithium hydroxide in an alcohol to form a lithium alkoxide. Vanadium pentoxide is then added and the mixture heated to form a precipitate, which is in the form of a fine powder. Yet another solvent based method is disclosed by Hammou et al., Electrochimica Acta, 13, 1719 (1988). This method uses an organic liquid, such as n-hexane, to ball mill a mixture of lithium carbonate and vanadium pentoxide powders. A solid state reaction is then carried out by heating this mixture at 590.degree. C. in air. It is generally undesirable to use organic liquids, and even water, however, because such methods typically require filtering, drying, and post-particle size reduction.
Dry solid state methods (i.e., those that do not involve the use of liquids) have been developed in an attempt to avoid the problems associated with methods that include the use of liquids, particularly organic liquids. For example, U.S. Pat. No. 5,520,903 (Chang et al.) discloses a method that involves combining particles of a lithium compound, such as lithium carbonate or hydroxide, and a vanadium compound, such as vanadium pentoxide, and compacting the mixture to a densified body. The densified body, which has a density of at least 50% of theoretical, is heated to below the melting point (typically no greater than about 600.degree. C.) to cause conversion to lithium vanadium oxide. It is disclosed that a minimum temperature of about 570.degree. C. is needed to achieve acceptable results. As with molten material, this densified material can be very difficult to grind to a material of suitable particle size and particle size distribution.
Lithium vanadium oxide has also been made in a solid state reaction by heating reactants in the form of free flowing particulate material at a temperature slightly below their melting points. However, upon heating to temperatures of about 550.degree. C. to 630.degree. C., for example, the free flowing particulate material can agglomerate and form clumps as a result of melt adhesion. JP 6-171947 (Mitsui Toatsu Chemicals, Inc.) discloses a method that solves this problem by heating the reactants in a rotating drum.
Many other methods for forming lithium vanadium oxide, as well as electrodes containing such material, involve multistep mixing, milling, and/or grinding techniques. These multistep processes are not generally desirable for large-scale manufacturing, however. Thus, what is needed is an improved method of making lithium vanadium oxide suitable for use in electrodes, for example, in cathodes of lithium batteries. Also, what is needed is an improved method of making cathodes that include lithium vanadium oxide.